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Topic Review (Newest First)
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| 04-25-2011 06:22 PM | ||
| dean2287 |
Re: St g-90 - tuned!! Thanks to 1THEPALMER and his spot-on advice, I now have the ST-90 tuned and running perfectly!! The fuel nipple on the carb MUST be pointing to the rearmost engine mounting hole. I messed aroung with the low speed needle for a while, but basically the method described is just about perfect. I turned it maybe 1/16 turn in from there. So now she's got a nice 1700 rpm idle, throttles up and down like a race car, has good mid-range performance , and is ready to pull the Beaver on her maiden. Thanks very much for the advice!! I love this website. 
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| 04-22-2011 12:33 AM | ||
| dean2287 |
Re: ST G-90 adjustment Thanks again guys, more excellent suggestions. I did not know about the mid range adjustment with the carb position.Many others have commented on how "fussy" this engine is to get adjusted, but also how great it is once properly set up. It should be worth the time invested. Besides, the way the weather has been this spring, I've got nothing but time to keep fiddling! |
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| 04-21-2011 03:07 PM | ||
| DO335 |
Re: ST G-90 adjustment [QUOTE=Waco Driver;821192]The Surertigre carb has provision for adjusting the midrange mixture. Loosen the 2 screws retaining the needle valve body to the carb. With the engine running in the midrange ,slowly turn the body anti-clockwise to lean the mixture. Tighten the screws to hold the desired setting.QUOTE] That's exactly how the ST carb is intended to be set for the mid range. As for your the idle and going dead coming off idle, you can die there for two reasons: #1. idle is too lean or #2. idle is too rich. How to tell the difference? Test and see what it does. Pay close attention. When going off idle, does it simply sag and die? IfF so, it's lean. Does it sag, belch out smoke and then pick up? If so, it's too rich. There are no other possibilities. This assumes that everything else is right - no air leaks, good plug, fresh fuel, appropriate size prop, no punctures in fuel line, no fuel starvation and that sort of thing. Adjust the idle needle only a bit at a time and retest until you have a good transition. Still have a problem in the mid range? Adjust the location of the fuel exit hole in the spray bar as Waco Driver advised. Once you learn your Tigre and get it set, you should find that it is very reliable and easy to run. |
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| 04-21-2011 08:08 AM | ||
| Waco Driver |
Re: ST G-90 adjustment The Surertigre carb has provision for adjusting the midrange mixture. Loosen the 2 screws retaining the needle valve body to the carb. With the engine running in the midrange ,slowly turn the body anti-clockwise to lean the mixture. Tighten the screws to hold the desired setting. I would suggest an APC 16x4W for the Beaver. I am using this prop on mine with an OS91FS and it looks and flies very scale like with this prop. |
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| 04-21-2011 12:40 AM | ||
| dean2287 |
Re: ST G-90 adjustment More run in today, a little better with some low speed needle adjustment and bigger prop. Got a decent idle at about 2800-3000 rpm, but still dying off a bit when throttling up. I tried a few adjustments to the low speed setting which admittedly didn't seem to do much, but it is better than before. Just needs more time I guess. The 14x6 is great on this engine, still spins at 10,600 rpm full throttle with a slightly rich mixture, and does give a better scale appearance to the Beaver. Engine seems happier with it. |
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| 04-16-2011 11:12 PM | ||
| dean2287 |
Re: ST G-90 adjustment Quote:
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| 04-16-2011 01:17 PM | ||
| 1THEPALMER |
Re: ST G-90 adjustment To set low speed needle on ST carb. 1) close throttle down with a pin in the venturi as a stop. 2) turn out high speed approx 3 turns 3) attach clean fuel line to fuel nipple 4) while blowing through fuel line turn in low speed needle until air just stops 5) take a breath, now blow (gently) again while turning out the low speed needle stoping when air just starts to move This will get you very close. Note how small the venturi opening is @ this point about 2..3 clicks more of throttle trim will be starting idle. To start prime until the engine is sloppy wet, hook up glow then bump gently backwards against compression. It should hit fire and take off running. Let it run (30 sec) with glow heat attached then go to full throttle. Leave glow heat on. Tweak the high speed needle, go to max. RPM then back off at least 200 RPM. Tach is a must for this or just go past a wet 4stroke. 3 to 3 1/2 turns never been less for me. drop throttle to idle, engine will now drop RMP slowly gurgling for some time as it burns off excess fuel then settles into a nice stable idle. Do not mess with the low speed!!!! this is as good as it gets with this carb. If you plan to fly this setup @ mid to low throttle settings glow heat will be a must otherwise it will die in the mid range from fuel loading. A "fix" for the mid range is an OS type D carb a perry carb or slightly modifing the ST carb. To do this you have to strip the carb and twist the spray bar opening about 15deg. off straight down. Some say back is best. Then put the whole thing back and start the tuning steps all over again. If you go the spray bar route be prepared to spend some time fiddling as it will take several tries to get things working. The way this has gone for me is move spray bar test... little change... move spray bar test.... some change..... move spray bar... test... ARGH motor now hardly runs. move spray bar back just a little test...best so far . Go fly. Good luck with it, the motor is a really old design and while makes a ton of power has never been good in the mid range. I have one on a Macs pipe and it screams but still no real mid range. Also a 2300 with a Jett carb. the mid range is "better" but still some burble but at least the engine will run for a full flight if you carefully advance the throttle from mid to high, forget and snap it up........silence every time. |
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| 04-16-2011 07:18 AM | ||
| g-manz35 |
Re: ST G-90 adjustment Quote:
I think you are on the right track. If an engine dies when you open the throttle you are probably lean. Mine idles quite well even if it is a bit rich. I notice you are getting some advice that differs slightly from my experience. Keep in mind that the ST 90 has been made for a long time and has gone through some changes. So take everything with a grain of salt ie "brake in" I did not find mine required a lot of break in time, but I have heard that some of the older ST engines did. My engine however is a G90 like yours. Great engine. Good luck. George |
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| 04-16-2011 04:34 AM | ||
| gcarabin |
Re: ST G-90 adjustment I have had a number of ST-90s over the years. Mainly on the Goldberg Extra 300 and the GBerg Ultimate. My favourite prop was a Graupner 13 1/2 x 8. Others in our club like a 14x7 prop. I guess it's all what you are comfortable with. My favourite thing with the ST90 is the "burble" it makes when throttling back to idle. GC |
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| 04-16-2011 02:17 AM | ||
| dean2287 |
Re: ST G-90 adjustment Wow...again guys, this is really good information. I can't thank you enough. I've been again hampered by the weather so I haven't had a chance to fire it up with the 14x6. I also think the low idle is too lean and will open it up 1/8 turn next time. I do think this engine will be great once broken in. A FA-100 would be really sweet for sure, but I'm already way over budget on this project! She's (ahem, cough cough) far from scale anyhow... Cheers All |
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